Seismic data recording

ABSTRACT

A seismic survey is conducted by positioning an array of remote acquisition units (RAUs). Each of the RAUs records seismic data derived torn one or more geophones in digital form in local memory. The data is collected by a harvester unit traversed across the survey territory as by an aircraft using point-multipoint communications, and subsequently transferred from the harvester unit to a central control unit.

This invention relates to seismic surveying, and in particular to amethod of acquiring seismic data, and to a system for use with such amethod.

BACKGROUND TO THE INVENTION

Conventionally, in land seismic surveys, an array of seismic sensors ispositioned to detest acoustic signal reflected from earth formations.The seismic sensors may fee either analogue geophones or digitalaccelerometers. The signals from these sensors are input to Field Unitswhere, in the case of analogue geophones, the signal is converted to ahigh-precision digital sample stream, and where with either type ofsensor the digital sample stream is transmitted in real-time over acommunications network to a Central Unit to be recorded on bulkrecording media. The communications network involved in this process maybe a cable-based network with repeaters and battery feeds as required;it may be an entirely cable-free network utilizing wireless techniquesto transfer the data; or the network may consist of elements of bothcabled and wireless technologies.

A number of disadvantages have keen identified with these conventionalsystems, which has led to the development of a number of land seismicacquisition systems which do not utilize a communications network totransfer the digital sample stream to a Central Unit for recording, butwhich instead record the data locally in the Field Unit in non-volatilememory. In the normal case, the Field Unit records the data locally foras long as its seismic sensors are required as part of the active sectorof the survey. The Field Units are then transported to a Central Unitfor connection to a transcription unit and subsequent uploading of thedata from the Field Unit to the Central Unit.

The primary advantages proposed for this technique are:

-   -   i. Reduction in manpower requirement as no communications        infrastructure needs to be deployed    -   ii. Increased productivity as acquisition is not delayed by        faults in a communications network

These advantages are mitigated, however, by a number of disadvantageswhich this invention seeks to address either wholly or in part. Thesedisadvantages are:

-   -   i. The non-volatile memory within the Field Unit must be large        enough to record all trio seismic data acquired while to Field        Unit is active on a survey, which may be as long as 14 days in a        normal survey, but in exceptional oases may be much longer and        may be indeterminate.    -   ii. It is normally the case that the Field Unit must be        transported to a data transcription system which will be used to        transfer all the acquired seismic data to the Central Data        Recorder.    -   iii. The seismic data acquired during the survey will not be        available for examination until all the Field Units have been        transcribed as described in ii above, which may ha as much as 14        days after the start of the survey, involving substantial risk        that poor quality date may be acquired before there is an        opportunity to detect it.    -   iv. There is a risk that Field Units may malfunction, be stolen,        or be misplaced during the survey involving the loss of all the        data acquired by them.    -   v. Substantial field crew effort is required to transport the        Field Units to the transcription system in a timely manner,        which impacts on the productivity of the survey.    -   vi. Unforeseen circumstances, such as bad weather conditions,        may delay transportation of the Field Units to the transcription        system, causing further delays to the processing of the data.

SUMMARY OF THE INVENTION

The invention, in one aspect, provides a method of uploading seismicdata from multiple remote acquisition units positioned across a surveyarea, each remote acquisition unit storing seismic data from one or moregeophones, the method comprising traversing a harvester unit across thesurvey area, the harvester unit including or being accompanied by apoint-multipoint transceiver, and uploading me seismic data from each ofthe remote acquisition units as the harvester unit passes within range,seismic data passing from more than one remote acquisition unit to theharvester unit simultaneously where necessary.

Preferably, the seismic data stored and transmitted by each of theremote acquisition units includes timestamp information relating to therelevant seismic event. The timestamp information may suitably bederived at the remote acquisition unit from an independent remote sourcesuch as GPS or terrestrial radio time signals.

The harvester unit may traverse the survey area in a vehicle such as anaircraft, vessel, ground-effect vehicle, or all-terrain wheeled ortracked vehicle.

Seismic data is preferably compressed by a lossless compressionalgorithm before being transmitted by the remote acquisition unit.

Preferably, each of the remote acquisition units is programmed toperiodically search for the presence of an access point the remoteacquisition unit reverting to an energy-saving state in the absence ofan access point.

From another aspect the invention provides a method of conducting aseismic survey, comprising positioning an array of remote acquisitionunits across a survey area, connecting one or more seismic sensors toeach of the acquisition units, performing one or more seismic events endstoring resetting seismic data from the seismic sensors in the remoteacquisition units, end uploading the stored data by the foregoingmethod.

Preferably, before data is acquired, each of the remote acquisitionunits is configured with parameters defining working hours andoptionally one or more of sample interval, amplifier gain and fittercharacteristics.

Each remote acquisition unit may be arranged to transmit to theharvester with only data relating to a start time and number of samplesas defined in a signal from the harvester unit to the remote acquisitionunit.

Optionally, the harvester unit extracts and transmits a limited data set(such as battery status, sensor status, and position) from each remoteacquisition unit for receipt by a central control unit during passage ofthe harvester unit across the survey area.

The seismic survey method preferably includes the further step ofuploading seismic dele from the harvester unit to a central unit, forexample by transporting the harvester unit to the central unit anddownloading via cable connection, or by downloading from the vehicleremotely to the central unit over a wireless data connection.

A further aspect of the present invention provides a seismic dataacquisition system comprising:

-   -   multiple remote acquisition units deployed in an array across a        survey area;    -   each of the remote acquisition units being in communication with        one or more geophones and including storage means for storing        seismic information from said geophone(s) in digital form, and        each of the remote acquisition units including a transceiver        adapted to operate in a point-multipoint wireless system;    -   whereby stored seismic data may be transmitted from the multiple        remote acquisition units to a point-multipoint transceiver of a        harvester unit as the latter is traversed across the survey        area.

The storage means in each of the remote acquisition units is mostsuitably a non-volatile memory.

Preferably, each of the remote acquisition units is adapted to associatea timestamp with a given set of seismic data, the timestamp beingderived from a timing signal resolved by wireless from a central unit orfrom GPS timing information.

The system typically includes a harvester unit with an associatedpoint-multipoint transceiver in a portable form capable of traversingthe survey area.

The harvester unit may be mounted in a vehicle such as helicopter, lightaircraft, either manned or remote controlled (UAV). Including microlightand other “experimental” aircraft, un-tethered blimp, either remotecontrolled or piloted, beat, including air-boats of the type typicallyused in swamps and marshland, hovercraft, or motor vehicle, includingpickup truck, all-terrain vehicles and quads; or in a backpack forpedestrian use.

The invention in another aspect provides harvester unit for use in theabove method or system, comprising a ruggedised field portable computeroperably coupled with a power source, a bulk storage memory, andpoint-multipoint communication access point and an antenna, all of theforegoing forming a transportable package suitable for being traversedacross a seismic survey terrain.

DETAILED DESCRIPTION

An embodiment of the invention will now be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1 is a schematic overview illustrating one embodiment of theinvention;

FIG. 2 shows one part of FIG. 1 in greater detail;

FIG. 3 is a block diagram of a harvester unit 28 used in the system ofFIG. 1;

FIG. 4 is a flow chart illustrating the operating method of theembodiment; and

FIG. 5 illustrates a modified embodiment.

Referring to FIG. 1, in carrying out a seismic survey, an array of FieldUnits or Remote Acquisition Units (hereinafter RAUs) to is arrangedacross a territory of interest. As seen in FIG. 2, each RAM 10 isconnected to one or more geophones 12.

Referring also to FIG. 2, each of the RAUs comprises ananalogue-to-digital converter 14 (in the ease of analog geophones), anda memory 16. The AD converter 14 performs a high-precision, 24-bitanalogue-to-digital conversion on the sensor signal. The memory 16 issuitably a non-volatile memory such as a hard disc drive or a flashmemory. The RAU 10 also comprises a time reference moans 10 which in apreferred form is a GPS receiver capable of deriving an accurate timereference from GPS transmissions; however in principle other sources oftime reference may be used, such as an accurate internal clock or areceiver for terrestrial time radio signals. The RAU 10 is self poweredby an internal source such as battery 20, and also comprises atransceiver 22 adapted to operate in a point-multipoint system. Thewireless transceiver 22 is preferably compliant with the IEEE802.11family of wireless standards particularly the IEEE802.11b, IEEE802.11g,IEEE802.11a, and IEEE802.11n standards operating in the 2.4 GHz or 5.8GHz frequency bands; however other transceivers such as Ultra Wide Banddevices, Bluetooth devices, VHF devices, UHF devices operating in the900 MHz, 2.4 GHz, 5.8 GHz, 60 GHz, 150 MHz-174 MHz, 400 MHz-470 MHzfrequency hands, or other frequency hands, whether compliant withstandards such as IEEE802.15 or using proprietary protocols may also beused.

Reverting to FIG. 1, the RAUs 10 operate autonomously to acquire andstore seismic information which is subsequently captured by a harvesterunit 28 which is traversed across the geophone territory, for example inan aircraft 24, all the data thus retrieved being subsequentlytransferred from the harvester unit 28 to a central unit 26. Thisprocess is described in more detail below.

The central unit 26 performs two functions. First, it is used toconfigure the RAUs 10, as discussed below. Secondly, the central unit 26uploads the seismic data, processes and merges if with any requisitedata from its source control database and generates seismic trace datain an SEG (Society of Exploration Geophysicists) compatible format.

FIG. 3 illustrates the harvester unit 28, which comprises the followingcomponents:

-   -   A portable, field-rugged, battery-powered computer 30 loaded        with the required software    -   A high capacity bulk data storage device 32 either incorporated        in the computer 30 or connected to it externally    -   A wireless access point 34 connected to the computer and        compatible wild the wireless transceivers 22 incorporated into        the RAUs. This should preferably communicate with the computer        30 using one of the following methods: wired Ethernet; USB;        wireless, where the computer has a compatible wireless        transceiver fitted internally.    -   An antenna 36.    -   Optionally, a battery-pack (38) to power these components. In        some instances the vehicle power system may be used to supply        power instead.    -   A mounting kit (not shown) to fit the above components to the        vehicle used to transport the harvester unit 28.

The process of recording is subject to a configuration procedure whichcan take place either before the RAUs 10 are deployed or subsequent todeployment. The RAUs 10 are connected by means of a cable or by awireless link to a computer from where operating parameters of the RAUsare configured. These parameters are the sample interval and workinghours, and optionally amplifier gain (analogue only) and filtercharacteristics (that is, characteristics of filtering applied to theseismic signal before being recorded). The working hours parameterdetermines the times of day during which the RAU 10 acquired and recordsdata from its sensors 12; at other times the RAU 10 enters a modewhereby power consumption is reduced to an absolute minimum. The otherparameters rotate to the manner in which the seismic data is acquiredfrom the sensors.

While the RAUs 10 are acquiring and recording data, they periodicallyswitch on the internal wireless module 22 and search for a wirelessaccess point which is transmitting a correct service set identifier. Ifno such transmitting access point is detected, the wireless module 22 isswitched off for a certain period of time, after which a renewed searchwill take place. The length of time that the wireless module 22 isswitched off is optimized in order to reduce the overall powerconsumption of the RAU 10, while maintaining an acceptable response timein the presence of a valid access point.

It will thus be seen that the RAUs 10 acquire seismic data during theconfigured working hours and store this data in non-volatile memory 16together with associated timestamp information derived from timing means18. This happens autonomously, without any communication with thecentral unit 26. The stored data is subsequently collected by theharvester unit 28 whenever the access point of the harvester unit 28 isidentified by the RAU 10.

The above procedure allows the field crew to be able to retrieverecorded seismic data from the RAUs 10 by the method described below.

The seismic field crew is equipped with the harvester unit 28 of FIG. 3.The wireless access point 34 acts as a point-multipoint wireless accesspoint compatible with the transceivers 22 in the RAUs 10, and transmitsa service set identifier which the RAUs 10 will recognize as valid.

The field crew connects the harvester unit 28 to the central unit 26from where the entire seismic operation, including control of theseismic sources is undertaken. The central unit 26 transfers a list tothe computer 30 containing the precise start time, and number ofsamples, of every seismic record of interest to be recorded. Thisprecise start time is hereafter referred to as the timebreak.

The field crew then proceeds across the prospect with the harvester unit28, which establishes communications with RAUs 10 as it comes withinwireless range of them. When a communications link is established, theharvester unit 28 transfers the timebreak and number of samples repairedfor each record to the RAU 10, which then transmits the requiredrecorded data to the harvester unit 28.

The method of the present embodiment is illustrated in FIG. 4.

The point-multipoint wireless access point 34 in the harvester unit 28may communicate with multiple RAUs 10 simultaneously, limited bywireless transmission range, vegetation and topology; however, alsolimited by the harvester software which is configured wild a maximumlimit of RAU connections to optimize the wireless data throughput.

The data throughput may be further optimized by the use of a losslesscompression algorithm to reduce the actual amount of data transferred.Various forms of lossless data compression are well known and may beused here. However, a particularly suitable form of compression isdescribed in WO03079039 (A2).

In the harvester unit 28, the data retrieved from the RAUs 10 is storedin the local bulk storage 32 such as a hard disk drive. After theharvester unit 28 has traversed the survey area, the harvested data istransferred to the central unit 26 by any suitable means, for example bytransporting the harvester unit 28 to the central unit 26 anddownloading via cable connection, or by downloading from the vehicleremotely to the central unit 26 over a wireless data connection.

In a modification, shown in FIG. 5, the harvester unit 28 isadditionally provided with a radio link such as VHF or UHF transceiver40 which is capable of effecting communication at a relatively low ratewith the central control unit 26 (as indicated by dashed line in FIG.1). As the harvester unit 28 is traversed across the survey terrain theseismic data is harvested and stored as before. In addition, however,the harvester unit 28 derives from the RAUs information which may bereferred to as qualify control (QC) data and transmits this to thecentral control unit 26 in real time.

The QC information will typically be battery power level and the statusof the RAU, plus optionally a GPS-derived position of the individualRAU. This will typically amount to a few kilobits of information, whichcan be transmitted over a simple VHF link in real time. The stains ofthe RAU will typically as a simple yes/no indication that the seismicsensor is working, for example that the correct number of geophone areconnected, or that a digital sensor has passed a built-in test sequence.

This modification allows the central control unit to have very quicklysome basic information about each of the RAUs, particularly the factthat it is operational and is acquiring seismic data. If the proportionof inoperative or defective RAUs exceeds a predetermined threshold, therelevant part of the seismic survey can be ignored or aborted withouttransferring and analysing large amounts of data.

The harvester unit 28 may be transported across the prospect by a numberof different means, examples of which are given below.

-   -   1. Helicopter    -   2. Light aircraft, either manned or remote controlled (UAV).        Including microlight and other “experimental” aircraft    -   3. Un-tethered blimp, either remote controlled or piloted    -   4. Boat, including air-heats of the type typically used in        swamps and marshland    -   5. Hovercraft    -   6. Motor vehicle, including pickup truck, all-terrain vehicles        and quad bikes    -   7. Backpack for pedestrian use.

It will be noted that in the present invention the RAUs operate in an“autonomous” mode, and perform the functions of data capture, storageand forwarding without any interaction with a Central Control Unit,relying on preconfigured parameters for pre-amplifier gain, sampleinterval end ether relevant settings. In this mode, timingsynchronisation is provided by a GPS receiver or a radio timing signalend thus also without any interaction with the Central Control Unit.

Point-multipoint transceivers suitable for use in the invention areknown per se. The data transfer rate typically required between the RAUand the harvester unit 28 is 11 Mbits/sec, and an example of a suitablepoint-multipoint transceiver for this application is the Abicom FreedomCPE by Abicom International of Market Drayton, Shropshire.

The invention thus provides a method and system which minimises thelabour involved in setting out a survey, makes retrieval of the seismicdata more convenient, and can operate with relatively limited memorycapacity in the RAUs owing to the ease of harvesting.

The invention claimed is:
 1. A method for transferring data, between acentral unit and plural remote acquisition units, by using a mobileharvester unit during a seismic survey, the method comprising:distributing the plural remote acquisition units over a survey area,wherein a remote acquisition unit is connected with a wire to one ormore seismic sensors; recording with the one or more seismic sensorsseismic data related to the survey area; storing the seismic data at theremote acquisition unit and transferring the seismic data to the centralunit; traversing the survey area with the mobile harvester unit;wirelessly collecting at the mobile harvester unit, while traversing thesurvey area, quality control data from the remote acquisition unit,wherein the quality control data is different from the seismic data; andtransmitting the quality control data from the mobile harvester unit tothe central unit during the seismic survey, wherein the central unit (1)configures the plural remote acquisition units and (2) processes theseismic data to generate seismic trace data compatible with Society ofExploration Geophysicists format.
 2. The method of claim 1, furthercomprising: receiving during a same pass, at the mobile harvester unit,the seismic data and the quality control data from a set of remoteacquisition units.
 3. The method of claim 1, wherein the quality controldata includes a battery power level, a seismic sensor status, and alocation of the remote acquisition unit.
 4. The method of claim 3,wherein locations of the remote acquisition units are determined bygeneral positioning systems (GPSs) located inside the remote acquisitionunits.
 5. The method of claim 1, wherein the quality control data isused to determine whether to transfer the seismic data to the centralunit.
 6. The method of claim 1, further comprising: based on the qualitycontrol data, determining in the central unit if a proportion ofinoperative or defective remote acquisition units exceeds apredetermined threshold; and ignoring seismic data corresponding to theinoperative or defective remote acquisition units.
 7. The method ofclaim 1, further comprising: based on the quality control data,determining in the central unit if a proportion of inoperative ordefective remote acquisition units exceeds a predetermined threshold;and instructing the mobile harvester unit to abort transferring seismicdata corresponding to the inoperative or defective remote acquisitionunits.
 8. The method of claim 1, further comprising: transmitting inreal time the quality control data from the mobile harvester unit to thecentral unit.
 9. The method of claim 1, further comprising: connectingthe mobile harvester unit to the central unit; downloading from thecentral unit onto the mobile harvester unit a list including a starttime and a number of samples of seismic records to be recorded by theplural remote acquisition units; traversing the survey area with themobile harvester unit; and wirelessly transferring to the plural remoteacquisition units the start time and the number of samples of seismicrecords to be recorded, wherein the start time indicates a time when theone or more seismic sensors must start to record the seismic data.
 10. Asystem for transferring data during a seismic survey, the systemcomprising: plural remote acquisition units distributed over a surveyarea and configured to record seismic data related to the survey area, aremote acquisition unit being connected with a wire to one or moreseismic sensors; a mobile harvester unit that traverses the survey areaand wirelessly collects quality control data, while traversing thesurvey area, from the plural remote acquisition units, wherein thequality control data is different from the seismic data; and a centralunit that receives the quality control data from the mobile harvesterunit during the seismic survey and also receives the recorded seismicdata, wherein the central unit (1) configures the plural remoteacquisition units and (2) processes the seismic data to generate seismictrace data compatible with Society of Exploration Geophysicists format.11. The system of claim 10, wherein the quality control data includesbattery power level, a seismic sensor status, and a location of theremote acquisition unit.
 12. The system of claim 11, wherein thelocation of the remote acquisition unit is determined by a generalpositioning system (GPS) located inside the remote acquisition unit. 13.The system of claim 10, wherein the mobile harvester unit comprises: awireless access point configured to receive the seismic data and thequality control data from the plural remote acquisition units; and aradio link configured to transmit the quality control data to thecentral unit during the seismic survey.
 14. The system of claim 13,wherein the wireless access point is configured to simultaneouslyreceive the seismic data from a set of remote acquisition units.
 15. Thesystem of claim 10, wherein the quality control data is used todetermine whether to transfer the seismic data to the central unit. 16.The system of claim 10, wherein the central unit is configured todetermine if a proportion of inoperative or defective remote acquisitionunits exceed a predetermined threshold, and to ignore parts of theseismic data corresponding to the inoperative or defective remoteacquisition units.
 17. The system of claim 10, wherein the central unitis configured to determine if a proportion of inoperative or defectiveremote acquisition units exceed a predetermined threshold, and toinstruct the mobile harvester unit to abort transferring parts of theseismic data corresponding to the inoperative or defective remoteacquisition units.
 18. The system of claim 10, wherein the qualitycontrol data is transmitted in real time between the central unit andthe mobile harvester unit.
 19. The system of claim 10, wherein prior tocollecting the seismic data, the mobile harvester unit is connected tothe central unit, a list is downloaded from the central unit onto themobile harvester unit, the list including a start time and a number ofsamples of seismic records to be recorded by the one or more seismicsensors, the mobile harvester unit traverses the survey area, and themobile harvester unit wirelessly transfers the start time and the numberof samples of seismic records to be recorded to the plural remoteacquisition units, wherein the start time indicates a time when the oneor more seismic sensors must start to record the seismic data.
 20. Amethod for transferring data, between a central unit and plural remoteacquisition units, by using a mobile harvester unit during a seismicsurvey, the method comprising: connecting the mobile harvester unit tothe central unit; downloading from the central unit onto the mobileharvester unit a list including a start time and a number of samples ofseismic records to be collected by the plural remote acquisition units;traversing the survey area with the mobile harvester unit; wirelesslytransferring the start time and the number of samples of seismic recordsto be recorded to the plural remote acquisition units; recording withone or more seismic sensors, attached with a wire to a remoteacquisition unit, seismic data related to the survey area andtransferring the seismic data to the central unit; transferring theseismic data and quality control data from the one or more seismicsensors to the remote acquisition unit; traversing again the survey areawith the mobile harvester unit; wirelessly collecting at the mobileharvester unit, while traversing the survey area, quality control datafrom the remote acquisition unit, wherein the quality control data isdifferent from the seismic data; and transmitting in real time thequality control data from the mobile harvester unit to the central unitduring the seismic survey, wherein the start time indicates a time whenthe one or more seismic sensors must start to record the seismic data,and wherein the central unit (1) configures the plural remoteacquisition units and (2) processes the seismic data to generate seismictrace data compatible with Society of Exploration Geophysicists format.21. The method of claim 1, further comprising: merging in the centralunit the seismic data with data from a source control database togenerate the seismic trace data.
 22. The system of claim 10, wherein thecentral unit merges the seismic data with data from a source controldatabase to generate the seismic trace data.